Cisco Switch

[alfonsocarledward]

Hi guys,

  I have a question regarding cisco switches, I don't know when to use switchport mode trunk, is it only used when for example, switch A is connected to switch B or it can also be used for switches connected to routers? I'm still having trouble in configuring switches.

  Another question is how can I configure a switch connected to a router with different vlans but can see each other, is it possible?

Thanks.

[Leo Laohoo]

Another question is how can I configure a switch connected to a router with different vlans but can see each other, is it possible? 

Configuring InterVLAN Routing and ISL/802.1Q Trunking on a Catalyst 2900XL/3500XL/2950 Switch Using an External Router

[devils_advocate]

If would be worth having a quick google on the difference between an Access Port and a Trunk Port, there are plenty of people who are a lot better at explaining things than I am :)

Generally a Trunk port is used between switches but can be used to connect a Switch with a Router or even a Switch with a Server. Both devices that you are connecting together need to be capable of 'tagging' packets before then send them across the link. 

Have a read up on Access and Trunk ports and then read up on Untagged and Tagged, if you can get round the concepts then you should understand L2 switching technology a bit better.

[Joseph W. Doherty]

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Posting

A (Cisco) switch trunk allows you to send have multiple VLANs use the port.  (VLANs, excluding native, are tagged so switch can tell them apart.)

On routers, you create a similar port by defining subinterfaces, each subinterface defined to use a certain VLAN tag.

(router) e.g.:

interface FastEthernet0/0
 description to switch trunk
 no ip address

interface FastEthernet0/0.1
 description vlan 1
 encapsulation dot1Q 1 native

  ip address 192.168.1.1 255.255.255.0

interface FastEthernet0/0.45
 description vlan 45
 encapsulation dot1Q 45
 ip address 192.168.45.1 255.255.255.0